On the Mechanism for the Extremely Efficient Sensitization of Yb3+ Luminescence in CsPbCl3 Nanocrystals

摘要： Rare earth (RE3+) doped inorganic CsPbX3 (X=Cl or Cl/Br) nanocrystals have been presented as promising materials for applications in solar-energy-conversion technology. An extremely efficient sensitization of Yb3+ luminescence in CsPbCl3 nanoparticles (NCs) was very recently demonstrated where quantum cutting is responsible for photoluminescence quantum yields over 100% (T. J. Milstein, et al., Nano Letters 2018, 18, 3792). In the present work, based on cubic phase of inorganic perovskite, we seek atom-level-insight into the basic mechanisms behind these observations in order to boost the further development of RE3+ doped CsPbX3 NCs for optoelectronics. In our calculations of cubic crystal structure, we do not find any energy level formed in the middle of the band gap, which disfavors a mechanism of step-wise energy transfer from the perovskite host to two Yb3+ ions. Our work indicates that the configuration with 'right-angle' Yb3+-VPb-Yb3+ couple are most likely to form in Yb3+-doped CsPbCl3. Associated with this 'right-angle' couple, the 'right-angle' Pb atom with trapped excited states would localize the photogenerated electrons and could act as the energy donor in a quantum cutting process, which achieves simultaneous sensitization of two neighboring Yb3+ ions.